U.S. patent number 4,618,552 [Application Number 06/700,973] was granted by the patent office on 1986-10-21 for light receiving member for electrophotography having roughened intermediate layer.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Fumio Sumino, Shigemori Tanaka, Hitoshi Toma.
United States Patent |
4,618,552 |
Tanaka , et al. |
October 21, 1986 |
Light receiving member for electrophotography having roughened
intermediate layer
Abstract
A light receiving member comprising an intermediate layer
between a substrate of a metal of an alloy having a reflective
surface and a photosensitive member, the reflective surface of said
substrate forming a light-diffusing reflective surface, and the
surface of said intermediate layer forming a rough surface. A light
receiving member comprising a subbing layer having a
light-diffusing reflective surface with an average surface
roughness of half or more of the wavelength of the light source for
image exposure provided between an electroconductive substrate and
a photosensitive layer.
Inventors: |
Tanaka; Shigemori (Tokyo,
JP), Sumino; Fumio (Tokyo, JP), Toma;
Hitoshi (Kawasaki, JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
|
Family
ID: |
26366334 |
Appl.
No.: |
06/700,973 |
Filed: |
February 12, 1985 |
Foreign Application Priority Data
|
|
|
|
|
Feb 17, 1984 [JP] |
|
|
59-28273 |
Mar 7, 1984 [JP] |
|
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59-42171 |
|
Current U.S.
Class: |
430/60; 430/4;
430/510; 430/58.05; 430/945 |
Current CPC
Class: |
G03G
5/10 (20130101); G03G 5/144 (20130101); G03G
5/102 (20130101); Y10S 430/146 (20130101) |
Current International
Class: |
G03G
5/10 (20060101); G03G 5/14 (20060101); G03G
005/14 () |
Field of
Search: |
;430/2,60,510,523,4,395,946 ;350/3.65,162.24,168 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Welsh; John D.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. A light receiving member comprising an intermediate layer
between a substrate of a metal or an alloy having a reflective
surface and a photosensitive layer, the reflective surface of said
substrate forming a light-diffusing reflective surface, and the
surface of said intermediate layer forming a rough surface having
an average surface roughness of about 0.5 to 30 .mu.m.
2. A light receiving member according to claim 1, wherein said
metal or alloy is aluminum.
3. A light receiving member according to claim 1, wherein the
light-diffusing reflective surface of said substrate has an average
surface roughness of .lambda./2 or more (.lambda.: wavelength of
the incident light during image exposure).
4. A light receiving member according to claim 1, wherein the
light-diffusing reflective surface of said substrate has an average
surface roughness of 0.5 .mu.m to 30 .mu.m.
5. A light receiving member according to claim 1, wherein the
light-diffusing reflective surface of said substrate has an average
surface roughness of 0.3 .mu.m to 20 .mu.m.
6. A light receiving member according to claim 1, wherein the rough
surface of said intermediate layer is formed by electroconductive
powder dispersed in a resin which forms said intermediate
layer.
7. A light receiving member according to claim 1, wherein the rough
surface of said intermediate layer has an average surface roughness
of .lambda./2 or more (.lambda.: wavelength of incident light
during image exposure).
8. A light receiving member according to claim 1, wherein the rough
surface of said intermediate layer has an average surface roughness
value less than the average surface roughness value of the
light-diffusing reflective surface of said substrate.
9. A light receiving member according to claim 1, wherein the
average surface roughness of said intermediate layer is 70% or
lower of the average surface roughness of the light-diffusing
reflective surface of said substrate.
10. A light receiving member according to claim 1, wherein the
average surface roughness of said intermediate layer is 10% to 40%
of the average surface roughness of the light-diffusing reflective
surface of said substrate.
11. An electrophotographic photosensitive member for
electrophotographic device employing laser beam as the light source
comprising an intermediate layer between a substrate of a metal or
an alloy having a reflective surface and a photosensitive layer,
the reflective surface of said substrate forming a light-diffusing
reflective surface, and the surface of said intermediate layer
forming a rough surface having an average surface roughness of
about 0.5 to 30 .mu.m.
12. An electrophotographic photosensitive member according to claim
11, wherein said metal or alloy is aluminum.
13. An electrophotographic photosensitive member according to claim
11, wherein the rough surface of said intermediate layer and the
light-diffusing reflective surface of said substrate have the
function of preventing generation of an interference fringe pattern
which appears during image formation.
14. An electrophotographic photosensitive member according to claim
11, wherein the rough surface of said intermediate layer is formed
by electroconductive powder dispersed in a resin which forms said
intermediate layer.
15. An electrophotographic photosensitive member according to claim
11, wherein said photosensitive layer has a laminated structure
comprising a charge generation layer and a charge transport
layer.
16. An electrophotographic photosensitive member according to claim
15, wherein said charge transport layer is laminated on the charge
generation layer.
17. An electrophotographic photosensitive member according to claim
11, wherein said intermediate layer has an electroconductive layer
having formed a rough surface and a barrier layer formed
thereon.
18. An electrophotographic photosensitive member according to claim
11, wherein said laser beam is a laser beam emitted from a
semiconductor laser.
19. A light receiving layer comprising a subbing layer having a
light-diffusing reflective surface with an average surface
roughness of about 0.5 to 30 .mu.m provided between an
electroconductive substrate and a photosensitive layer.
20. A light receiving member according to claim 19, wherein the
electroconductive substrate having the subbing layer has optical
characteristics which cause light-diffusing reflection at an
intensity of 50% or more relative to the intensity of the light
from the light source for image exposure.
21. A light receiving member according to claim 19, wherein the
electroconductive substrate having the subbing layer has optical
characteristics which cause light-diffusing reflection at an
intensity of 65% or more relative to the intensity of the light
from the light source for image exposure.
22. A light receiving member according to claim 19, which is formed
by forming a coating separated in micro-phases by coating an
electroconductive substrate with a mixture obtained by mixing
solutions of two kinds of resins incompatible with each other, then
removing one of said two kinds of resins by dissolution to form a
rough surface with the remaining resin, followed by formation of a
photosensitive layer thereon.
23. An electrophotographic photosensitive member for use in
electrophotographic device provided with laser beam as the exposure
light source, said electrophotographic photosensitive member
comprising an electroconductive substrate, a photosensitive layer,
and a subbing layer having an average surface roughness of about
0.5 to 30 .mu.m between said electroconductive substrate and
photosensitive layer.
24. An electrophotographic photosensitive member according to claim
23, wherein the electroconductive substrate having the subbing
layer has optical characteristics which cause light-diffusing
reflection at an intensity of 50% or more relative to the intensity
of the laser beam from the light source for image exposure.
25. An electrophotographic photosensitive member according to claim
23, wherein the electroconductive substrate having the subbing
layer has optical characteristics which cause light-diffusing
reflection at an intensity of 65% or more relative to the intensity
of the laser beam from the light source for image exposure.
26. An electrophotographic photosensitive member according to claim
23, which is formed by forming a coating separated in micro-phases
by coating an electroconductive substrate with a mixture obtained
by mixing solutions of two kinds of resins incompatible with each
other, then removing one of said two kinds of resins by dissolution
to form a rough surface with the remaining resin, followed by
formation of a photosensitive layer thereon.
27. An electrophotographic photosensitive member according to claim
23, wherein said photosensitive layer has a laminated structure of
a charge generation layer and a charge transport layer.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a light receiving member such as an
electrophotographic photosensitive member, more particularly to a
light receiving member suitable for an electrophotographic printer
of the system in which a laser beam is subjected to imagewise line
scanning, especially an electrophotographic photosensitive member
for laser printer.
2. Description of the Prior Art
Heretofore, the laser beam which has been employed for an
electrophotographic printer of the system by line scanning of laser
beam was a gas laser with relatively shorter wavelength such as
helium-cadmium laser, argon laser or helium-neon laser, and the
electrophotographic photosensitive member used therefor was a
CdS-binder type photosensitive layer having a large thickness or a
charge transfer complex (IBM Journal of the Research and
Development, January, 1971, P. 75-89). Accordingly, no multiple
reflection of laser beam occurred within the photosensitive layer
and hence no image of interference fringe pattern appeared
practically during image formation.
Whereas, for the purpose of minituarization and designing at low
cost of the device, a semiconductor laser has been utilized in
recent years in place of the gas laser as mentioned above. Such a
semiconductor laser, which has generally an oscillated wavelength
in the longer wavelength region of 750 nm or higher, requires an
electrophotographic photosensitive member having high sensitivity
characteristic in the longer wavelength region, and
electrophotographic photosensitive members for this purpose have
been developed.
As the photosensitive member having sensitivity to the longer
wavelength light (e.g. 600 nm or longer) known in the art, there
may be included, for example, a lamination type electrophotographic
photosensitive member having a laminated structure of a charge
generation layer containing a phthalocyanine pigment such as copper
phthalocyanine, aluminum chloride phthalocyanine, etc. and a charge
transport layer, or electrophotographic photosensitive member using
a selenium-tellurium film.
When such a photosensitive member having sensitivity to the longer
wavelength light is mounted on an electrophotographic printer of
the laser beam scanning system and subjected to laser beam
exposure, an interference fringe pattern appears in the toner image
formed, thus having a drawback that no good reproduced image can be
formed. One of the reasons conceivable may be due to incomplete
absorption of the laser with longer wavelength, which gives rise to
right reflection of the transmitted light against the substrate
surface and results in generation of multiple reflected light of
the laser beam, with the result that interference occurs between
such multiple reflected light and the reflected light on the
surface of the photosensitive layer.
As the method for cancelling this drawback, it has heretofore been
proposed to cancel multiple reflection occurring within the
photosensitive layer by way of roughening of the surface of an
electroconductive substrate employed in an electrophotographic
photosensitive member according to the anodic oxidation method or
the sant blast method, or providing a light-absorptive layer or a
reflection preventive layer between the photosensitive layer and
the substrate. However, no such method could cancel completely the
interference fringe pattern appearing as a practical problem during
image formation. Particularly, in the method wherein the surface of
the electroconductive substrate is roughened, it is required to
have an average surface roughness with a sufficient size in order
to cancel the interference fringe pattern which appears during
image formation. Whereas, according to the sand blast method, the
maximum surface roughness will be increased as the average surface
roughness is increased, and there is also a tendency that the
amount of greater roughness is increased in the distribution of its
roughness. For this reason, the portion with greater roughness will
function as the portion for injecting carriers into the
photosensitive layer, thus causing undesirable formation of white
dots (black dots when employing a reversal developing system).
Moreover, in the case of a great average surface roughness, it is
difficult to produce electroconductive substrates having a
roughened surface within a permissible range of average surface
roughness with good yield in the same lot in manufacturing, and
there remain a number of points to be improved. Also, in the method
employing a light-absorptive layer or a reflection preventive
layer, the interference fringe pattern cannot sufficiently be
cancelled, and yet there is also involved the drawback that the
manufacturing cost is increased.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel light
receiving member (e.g. electrophotographic photosensitive member),
particularly an electrophotographic photosensitive member for laser
printer, which has cancelled the drawbacks as described above.
Further, a primary object of the present invention is to provide an
electrophotographic photosensitive member, which has cancelled the
interference fringe pattern which appears during image formation
and appearance of black dots during reversal developing at the same
time and completely.
The present inventors, in view of the fact that roughening of the
surface of a substrate to an extent necessary for cancelling the
interference fringe pattern which appears during image formation
will rather increase the number of white dots (which appear as
black dots when employing reversal developing system) during image
formation depending on the extent of the roughened surface to give
a very bad copy, have found that by making the surfaces of the
substrate and the electroconductive layer roughened to the extent
as to generate no white dot or black dot as mentioned above, the
interference fringe pattern can also be prevented at the same time,
to accomplish the present invention.
Accordingly, such objects of the present invention can be achieved
by a light receiving member comprising an intermediate layer
between a substrate of a metal or an alloy having a reflective
surface and a photosensitive member, the reflective surface of said
substrate forming a light-diffusing reflective surface and the
surface of said intermediate layer forming a rough surface, or by a
light receiving member comprising a subbing layer having a
light-diffusing reflective surface with an average surface
roughness of half or more of the wavelength of the light source for
image exposure provided between an electroconductive substrate and
a photosensitive layer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of an electrophotographic photosensitive
member of the prior art;
FIG. 2 and FIG. 3 are schematic illustrations showing the optical
path of the light incident on the electrophotographic
photosensitive member of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The "average surface roughness" as herein mentioned refers to the
value as measured by a universal surface shape measuring
instrument, "SE-3C" produced by Kosaka Kenkyusho, Japan.
FIG. 1 and FIG. 2 show schematically the embodiments when
electrophotographic members are irradiated with a laser beam as the
coherent light. FIG. 1 is an example when employing an
electrophotographic photosensitive member of the prior art and FIG.
2 an example when employing the electrophotographic photosensitive
member of the present invention.
In FIG. 1, when a laser beam I.sub.1 is irradiated on the
photosensitive layer 3 of an electrophotographic photosensitive
member, a reflected light R.sub.1 is generated on the surface of
the photosensitive layer 3, and further the laser beam I.sub.2
transmitted through the inner portion of the photosensitive layer 3
of the laser beam I.sub.1 reaches the surface of the
electroconductive substrate 1, where another reflected light
R.sub.2 is generated. Then, interference occurs between R.sub.1 and
R.sub.2, and the reflected light R.sub.2 gives rise to multiple
reflections in the inner portion of the photosensitive layer 3, to
result in appearance of an interference fringe pattern during image
formation.
In contrast, in the embodiment of the present invention as shown in
FIG. 2, a subbing layer 2 is formed between the electroconductive
substrate 1 and the photosensitive layer 3, with the surface of the
subbing layer 2 being subjected to roughening working to form a
roughened surface 4. Thus, the light beam I.sub.1 incident during
image exposure is reflected against the surface of the
photosensitive layer 3 to generate a reflected light R.sub.1, while
it is transmitted as the light I.sub.2 through the inner portion of
the photosensitive layer 3 to generate diffusing reflected light
R.sub.3 on the surface of the roughened surface 4. The diffusing
reflected light R.sub.3 also includes the light, which is
transmitted through the inner portion of the subbing layer 2,
reflected against the surface of the electroconductive substrate 1
and then generated again as the diffused light on the roughened
surface 4. The diffusing reflected light R.sub.3, by having an
intensity at a ratio of 50% or more, preferably 60% or more,
relative to the intensity of the incident light I.sub.1, can
inhibit the interference between the reflected light R.sub.2 and
the diffusing reflected light R.sub.3 to the extent so as to enable
cancellation of the interference fringe pattern during image
formation.
For giving a diffusing reflected light R.sub.3 having an intensity
of 50% or more, preferably 60% or more, relative to the intensity
of the incident light I.sub.1, the roughened surface 4 of the
subbing layer 2 is required to be set at .lambda./2 or more
(.lambda.: wavelength of incident light I.sub.1), specifically at
an average surface roughness of 0.5 um or more, preferably within
the range from 0.6 um to 30 um.
When the ratio of the intensity of the diffusing reflected light
R.sub.3 to that of the incident light I.sub.1 is 50% or below, the
interference fringe pattern appearing during image formation cannot
sufficiently be cancelled.
Also, if the average surface roughness of the roughened surface 4
is made more than 30 um, white dots or black dots will appear
during, for example, image formation, whereby there is involved the
problem that no good copied image can be obtained.
According to a preferred embodiment of the present invention, the
roughened surface 4 formed on the subbing layer 2 should preferably
be one utilizing the so called micro-phase separation phenomenon.
Specifically, by coating an electroconductive substrate with a
mixture of solutions of two resins with no or very small
compatibility and, after drying, applying dissolving treatment with
a solvent which can dissolve selectively one of the resins, a
subbing layer 2 having a surface unevenness with any desired size
and density can be provided. According to this method, the size of
the unevenness constituting the roughened surface 4 can be
controlled by the thickness of the coating, and its density by the
mixing ratio of the two kinds of the resin solutions, and also with
an advantage in cost.
As the combination of the resins constituting the subbing layer 2
having the roughened surface 4, there may be included those
satisfying the following points:
(1) compatibility between the two resins should be small;
(2) the residual resin should have good adhesion to the
electroconductive substrate;
(3) the residual resin should have good resistance to the solvent
used in the above coated layers such as the photosensitive layer
3;
(4) the residual resin should have an electrical resistance of
about 10.sup.13 ohm.multidot.cm or lower in terms of volume
resistivity.
Specific examples of combination of resins satisfying the above
conditions may include combinations of phenol resins with polyamide
resins, combinations of epoxy resins with cellulose resins, etc.,
and the mixing ratio, which may differ depending on the size and
density of the unevenness required, may preferably be about 5% to
30% of the resin to be dissolved away relative to the residual
resin, with the film thickness being suitably about 0.3.mu. to
10.mu..
The subbing layer 2 having the roughened surface 4 of
light-diffusing reflectivity is made of a phenol resin, a polyamide
resin, an epoxy resin, a cellulose resin, etc., having a volume
resistivity of 10.sup.13 ohm.multidot.cm or less, in order to
maintain electroconductivity with the substrate, and can be
provided according to the forming method as described above. For
example, by mixing a phenol resin and a polyamide resin in an
alcoholic solvent, a resin dispersion containing the polyamide
resin solution dispersed as liquid droplets with diameters of about
1 to 3.mu. in the phenol resin solution can be obtained. The resin
dispersion is applied on the electroconductive substrate 1, and
after drying an curing, the coated substrate is dipped in a hot
alcoholic solvent, whereby only the polyamide resin is dissolved
away to obtain a coating of the cured phenol resin having an
unevenness of about 1.mu.on the electroconductive substrate 1.
Thus, the surface 4 of the subbing layer 2 is made to have a
surface roughness of .lambda./2 or more (.lambda.: wavelength of
the laser beam).
It is also possible in the present invention to provide another
subbing layer (not shown) between the subbing layer 2 and the
photosensitive layer 3, and it can be formed of, for example,
casein, polyvinyl alcohol, nitrocellulose, ethyleneacrylic acid
copolymer, polyamide (nylon 6, nylon 66, nylon 610, copolymerized
nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin, etc.
The film thickness of this layer may appropriately be 0.1 .mu.m to
5 .mu.m, preferably 0.5 .mu.m to 3 .mu.m.
According to a preferred example of the present invention, the
photosensitive layer 3 can be made to have a layered structure
comprising a charge generation layer and a charge transport
layer.
The charge generation layer in the present invention is formed by
dispersing a charge generating material selected from azo pigments
such as Sudan Red, Dian Blue, Janus Green B, etc.; quinone pigments
such as Algol Yellow, Pyrene Quinone, Indanthrene Brilliant Violet
RRP, etc.; quinocyanine pigments; perylene pigments; indigo
pigments such as indigo, thioindigo, etc.; bisbenzoimidazole
pigments such as Indofast Orange toner, etc.; phthalocyanine
pigments such as copper phthalocyanine,
Aluminochloro-phthalocyanine, etc.; quinacridone pigments; or
azulene compounds in a binder resin such as polyester, polystyrene,
polyvinyl butyral, polyvinyl pyrrolidone, methyl cellulose,
polyacrylates, cellulose esters, etc. Its thickness may be about
0.01 to 1.mu., preferably 0.05 to 0.5.mu..
On the other hand, the charge transport layer may be formed by
dissolving a positive hole transporting material selected from
compounds having in the main chain or the side chain a polycyclic
aromatic ring such as anthracene, pyrene, phenanthrene, coronene,
etc. or a nitrogen-containing hetero ring such as indole,
carbazole, oxazole, isoxazole, thiazole, imidazole, pyrazole,
oxadiazole, pyrazoline, thiadiazole, triazole, etc., and hydrazone
compounds in a resin having a film-forming property. This is
because charge transporting materials are generally low in
molecular weights and themselves poor in film-forming property.
Such resins may include polycarbonate, polymethacrylates,
polyarylate, polystyrene, polyester, polysulfone,
styrene-acrylonitrile copolymer, styrene-methyl methacrylate
copolymer, etc.
The thickness of the charge transport layer may be 5 to 20.mu.. It
is also possible to form a photosensitive layer 3 with a structure
having the charge generation layer as described above laminated on
the charge transport layer.
The photosensitive layer 3 is not limited to the modes as described
above, but there may also be employed, for example, photosensitive
layers, in which a charge transfer complex comprising
polyvinylcarbazole and trinitrofluorenone as disclosed in IBM
Journal of the Research and Development, January, 1971, p. 75-p. 89
supra, or a pyrylium compound as disclosed in U.S. Pat. Nos.
4,315,983 and 4,327,169 is used, or a photosensitive layer
containing a well-known inorganic photoconductive material such as
zinc oxide or cadmium sulfide dispersed in a resin, or a vapor
deposited film of selenium or selenium-tellurium, etc.
As the electroconductive substrate 1, a metal such as aluminum,
copper, stainless steel, etc. or a plastic having a metal vapor
deposited thereon may be suitable.
As the surface conditions of the substrate and the
electroconductive layer to be used in the electrophotographic
photosensitive member according to another preferred embodiment of
the present invention, it may be possible to use one having an
average surface roughness of .lambda./2 or more (.lambda.: the
wavelength of the incident light during image exposure) (preferably
0.5 .mu.m to 30 .mu.m, particularly preferably 0.3 .mu.m to 20
.mu.m).
As a preferable example of the present invention, the sum of the
average surface roughness of the substrate and the average surface
roughness of the electroconductive layer may suitably be .lambda./2
or more (.lambda.: the wavelength of the incident light during
image exposure), preferably 0.5 .mu.m to 30 .mu.m, particularly
preferably 0.3 .mu.m to 20 .mu.m. It is thereby preferred to set
the average surface roughness of the electroconductive layer at a
value lower than that of the substrate, specifically at a value 70%
or less, particularly preferably 10% to 40%, of the average surface
roughness of the substrate.
Also, as the surface condition of the substrate or the
electroconductive layer, it is suitable to use one in which about 1
to 30, preferably about 5 to 15, projections are formed per 1000
.mu.m.
If the sum of the average surface roughness of the substrate and
that of the electroconductive layer is in excess of 30 .mu.m, the
maximum surface roughness comes beyond 100 .mu.m, and the barrier
layer formed on the electroconductive layer cannot cover completely
over the projected portions forming the roughened surface, whereby
injection of carriers occurs at the projected portions into the
photosensitive layer, with the result that the carrier injected
portions appear as white dots undesirably during image formation
(black dots appear in the case of reversal developing).
On the other hand, in the case of the sum of average surface
roughnesses less than .lambda./2, generation of interference fringe
pattern during image formation cannot sufficiently be
cancelled.
As the roughening working method to be used in preparation of the
electrophotographic photosensitive member of the present invention,
there may be employed the sand blast method, the brush polishing
method and the anodic oxidation method. Particularly, roughening
can be effected by the sand blast method, in which glass beads of
about 0.1 mm to 1 mm in diameter are blasted against the surface of
a substrate or an electroconductive layer together with an air
pressure of, for example, 1 kg/cm.sup.2 to 10 kg/cm.sup.2, or the
method as disclosed in Japanese Patent Publication No. 5125/1982,
namely the method in which the substrate after anodic oxidation
treatment is dipped in an aqueous solution of an alkali metal
silicate. The above anodic oxidation treatment may be practiced by
passing current through an electroconductive substrate in an
aqueous or non-aqueous solution of an inorganic acid such as
phosphoric acid, chromic acid, sulfuric acid, boric acid, etc. or
an organic acid such as oxalic acid, sulfamic acid, etc.
FIG. 3 represents an electrophotographic photosensitive member
according to a preferred embodiment of the present invention. As
the electroconductive substrate 31 having a roughened surface 32 on
which projections 39 are formed, there may be employed a metal such
as aluminum, brass, copper, stainless steel, etc., or a film having
aluminum, tin oxide, indium oxide, etc. vapor deposited on a
plastic such as polyester. Its shape may be either a cylinder,
sheet or plate.
As the electroconductive layer 33 having a roughened surface 34 on
which projections 30 are formed, it is possible to use a vapor
deposited film of an electroconductive metal such as aluminum, tin,
gold, etc. or coated film containing electroconductive powder
dispersed in a resin. The electroconductive powder to be used in
this case may include metallic powder of aluminum, tin, silver,
etc., carbon powder and electroconductive pigments composed mainly
of metal oxides such as titanium oxide, barium sulfate, zinc oxide,
tin oxide, etc. A light absorber may also be contained in the
electroconductive layer 33.
The resin for dispersing an electroconductive pigment may be any
kind of resins, which can satisfy the conditions of (1) having firm
adhesion to the substrate, (2) having good dispersibility of powder
and (3) having sufficient solvent resistance. In particular, it is
suitable to use thermosetting resins such as curable rubber,
polyurethane resin, epoxy resin, alkyd resin, polyester resin,
silicone resin, acrylic-melamine resin, etc. The resin containing
an electroconductive pigment dispersed therein should have a volume
resistivity of 10.sup.13 ohm.multidot.cm or less, preferably
10.sup.12 ohm.multidot.cm or less. For this purpose, it is
desirable that the electroconductive pigment is contained at a
proportion of 10 to 60% by weight in the coated film. As the method
for dispersing electroconductive powder in a resin, it is possible
to use conventional methods by means of roll mill, ball mill,
vibrating ball mill, attritor, sand mill, colloid mill, etc. In the
case when the substrate is shaped in a sheet, wire bar coating,
blade coating, knife coating, roll coating or screen coating may
suitably be employed, while dip coating is suitable in the case of
a cylindrical substrate.
The electroconductive layer 33 may be formed to have a film
thickness generally of 1 .mu.m to 50 .mu.m, preferably of 5 .mu.m
to 30 .mu.m.
Between the electroconductive layer 33 and the photosensitive layer
38, there is provided a barrier layer 35 having the barrier
function and the adhesion function. The barrier layer 35 may be
formed of casein, polyvinyl alcohol, nitrocellulose,
ethylene-acrylic acid copolymer, polyamide (nylon 6, nylon 66,
nylon 610, copolymerized nylon, alkoxymethylated nylon, etc.),
polyurethane, gelatin, etc.
The film thickness of the barrier layer 35 can be made to 2-fold or
more of the average surface roughness of the roughened surface 34
formed on the electroconductive layer 33, specifically 0.1 to
10.mu., preferably 0.5 to 5.mu..
The photosensitive layer 38 can be made to have a layered structure
comprising a charge generation layer 36 and a charge transport
layer 37. The charge generation layer 36 is formed by dispersing a
charge generating material selected from azo pigments such as Sudan
Red, Dian Blue, Janus Green B, etc.; quinone pigments such as Algol
Yellow, Pyrene Quinone, Indanthrene Brilliant Violet RRP, etc.,
quinocyanine pigments; perylene pigments; indigo pigments such as
indigo, thioindigo, etc.; bisbenzoimidazole pigments such as
Indofast Orange toner, etc.; phthalocyanine pigments such as copper
phthalocyanine, Aluminochlorophthalocyanine, etc.; quinacridone
pigments; or azulene compounds in a binder resin such as polyester,
polystyrene, polyvinyl butyral, polyvinyl pyrrolidone, methyl
cellulose, polyacrylates, cellulose esters, etc. Its thickness may
be about 0.01 to 1.mu., preferably 0.05 to 0.5.mu..
On the other hand, the charge transport layer 37 may be formed by
dissolving a positive hole transporting material selected from
compounds having in the main chain or the side chain a polycyclic
aromatic ring such as anthracene, pyrene, phenanthrene, coronene,
etc. or a nitrogen-containing hetero ring such as indole,
carbazole, oxazole, isoxazole, thiazole, imidazole, pyrazole,
oxadiazole, pyrazoline, thiadiazole, triazole, etc., and hydrazone
compounds in a resin having a film-forming property. This is
because charge transporting materials are generally low in
molecular weights and themselves poor in film-forming property.
Such resins may include polycarbonate, polymethacrylates,
polyarylate, polystyrene, polyester, polysulfone,
styrene-acrylonitrile copolymer, styrene-methyl methacrylate
copolymer, etc.
The thickness of the charge transport layer 37 may be 5 to 20.mu..
It is also possible to form a photosensitive layer 38 with a
structure having the charge generation layer 36 as described above
laminated on the charge transport layer 37.
The photosensitive layer 38 is not limited to the modes as
described above, but there may also be employed, for example,
photosensitive layers, in which a charge transfer complex
comprising polyvinylcarbazole and trinitrofluorenone as disclosed
in IBM Journal of the Research and Development, January, 1971, p.
75-p. 89 supra, or a pyrylium compound as disclosed in U.S. Pat.
Nos. 4,315,983 and 4,327,169 is used, or a photosensitive layer
containing a well-known inorganic photoconductive material such as
zinc oxide or cadmium sulfide dispersed in a resin, or a vapor
deposited film of selenium or selenium-tellurium, etc.
The electrophotographic photosensitive member of the present
invention can be used for an electrophotographic system printer
employing a semiconductor laser with a relatively longer wavelength
(e.g. 750 nm or longer), but it is also suitable for use in
electrophotographic system printers employing other laser beams
such as helium-neon laser, helium-cadmium laser or argon laser. The
present invention, in addition to the advantage of cancelling
completely the interference fringe pattern during image formation
which has appeared in the prior art method when employing a
coherent light such as laser beam as the light source, has also the
advantage of cancelling effectively the black dots.
That is, generally speaking, in an electrophotographic system
printer employing a laser beam, a reversal developing system is
employed, in which after charging of the electrophotographic
photosensitive member, an electrostatic latent image is formed on a
back image by giving laser beam a posi-imagewise scanning exposure
(image scanning exposure) corresponding to image signals, and
subsequently by giving a developer having a toner of the same
polarity as the polarity possessed by the electrostatic latent
image to the electrostatic latent image surface, the toner is
attached onto the posiimagewise exposed portion subjected to image
scanning. In the case of such a reversal developing system,
unnecessary toner attachment occurred in black dots in the image
formed. This is because no uniform roughened surface can be formed
in the roughened surface formed by the sand blast method as
described above, with a great distribution between the projections
with small height and the projections with large height, whereby
carriers are injected from the unnecessarily great projections into
the charge generation layer to effect electrical neutralization
between the carriers injected from the projections and the charges
formed during charging, thus creating a state already electrically
subjected to imagewise exposure, to give rise to attachment of the
toner during development which causes formation of black dots.
In contrast, in the present invention, by use of an
electroconductive substrate having a roughened surface and an
electroconductive layer having a roughened surface, the
interference fringe pattern which appeared during image formation
in the prior art method and generation of black dots can be
cancelled at the same time. This point is to be described in detail
in the following Examples. Of course, the present invention is not
limited to the reverse developing system, but various kinds of
developing methods, such as the cascade developing method, the
magnetic brush developing method, the powder cloud method, the
jumping developing method and the liquid developing method and
others may also be available.
The present invention is described by referring to the following
Examples.
EXAMPLE 1
On the surface of a cylindrical aluminum of 60 mm in diameter and
258 mm in length, sand blast working was applied by blasting
spherical glass beads powder with an average diameter of 0.5 mm
containing 18% by weight of spherical glass beads of 1 mm or more
in diameter under an air pressure of 5 kg/cm.sup.2. The surface of
the thus sand blast worked cylindrical aluminum was measured by a
universal surface shape measuring instrument, "SE-3C" produced by
Kosaka Kenkyusho to find that the average surface roughness was 8
.mu.m.
Next, 25 parts by weight of titanium oxide (ECT-62, produced by
Titanium Kogyo K.K.), 25 parts by weight of titanium oxide (SR-1T,
produced by Sakai Kogyo K.K.) and 50 parts of a phenol resin
(Plyofen J325, produced by Dainippon Ink K.K.) were mixed with 500
parts by weight of methanol and methyl cellosolve (methanol/methyl
cellosolve=4 wt. parts/15 wt. parts) and stirred, followed by
dispersion together with 50 parts by weight of glass beads of 1 mm
in diameter by means of a sand mill dispersing machine for 10
hours.
The coating liquid for formation of electroconductive layer was
applied by dipping on the surface of the sand blast worked
cylindrical aluminum to a dried film thickness of 20 .mu.m,
followed by drying by heating, at 140.degree. C. for 30 minutes, to
form an electroconductive layer. The surface was measured by a
universal surface shape measuring instrument "SE-3C" produced by
Kosaka Kenkyusho to find that the average surface roughness was 1.5
.mu.m.
Subsequently, 10 parts of a copolymerized nylon resin (trade name:
Amilan CM-8000, produced by Toray K.K.) were dissolved in a mixture
comprising 60 parts by weight of methanol and 40 parts by weight of
butanol, and applied by dipping on the above electroconductive
layer to provide a polyamide resin layer with a thickness of
3.5.mu. thereon.
As the next step, 1 part by weight of .epsilon.-type copper
phthalocyanine (Linol Blue ES, produced by Toyo Ink K.K.), 1 part
by weight of a butyral resin (Eslec BM-2, produced by Sekisui
Kagaku K.K.) and 10 parts by weight of cyclohexanone were dispersed
in a sand mill dispersing machine containing 1 mm .phi. glass beads
for 20 hours, and thereafter diluted with 20 parts by weight of
methyl ethyl ketone. The dispersion was applied by dip coating on
the polyamide resin layer previously formed to form a charge
generation layer. The layer thickness was found to be 0.3.mu..
Then, 10 parts by weight of a hydrazone compound having the
following formula: ##STR1## and 15 parts of a styrene-methyl
methacrylate copolymer resin (trade name: MS 200, produced by
Seitetsu Kagaku K.K.) were dissolved in 80 parts by weight of
toluene. The solution was applied on the above charge generating
layer and dried by hot air at 100.degree. C. for one hour to form a
charge transport layer with a thickness of 16.mu..
The thus prepared electrophotographic photosensitive member was
mounted on Canon laser beam printer (LBP-CX, produced by Canon
K.K.) which is a reversal developing system electrophotographic
printer equipped with a semiconductor laser with an oscillated
wavelength of 778 nm, and then line scanning was conducted on the
whole surface to form an image of the whole surface with a black
toner image. As the result, no interference fringe pattern appeared
in the whole black image at all.
Next, the operation of forming letters as the image by line
scanning of laser beam following letter signals was repeated for
2000 times under the conditions of a temperature of 15.degree. C.
and a relative humidity of 10%, and the copied letter image of the
2000th sheet was taken out. When the number of the black dots with
diameters of 0.2 mm or more was measured in the copied letter
image, no dot was found at all.
An electrophotographic photosensitive member was also prepared
according to the same method except for changing the film thickness
of the polyamide resin used in preparation of the above
electrophotographic photosensitive member to 2 .mu.m, and the same
test was conducted. As the result, the number of black dots was
found to be increased in the 2000th sheet of the copied letter
image.
COMPARATIVE EXAMPLE 1
As the comparative test, in place of the cylindrical aluminum of
which surface was worked by the sand blast method employed in
preparation of the electrophotographic photosensitive member of
Example 1, a cylindrical aluminum was employed having mirror
surface characteristic, following otherwise entirely the same
procedure as in Example 1, to prepare an electrophotographic
photosensitive member.
The electrophotographic photosensitive member for comparative
purpose was mounted on the laser beam printer employed in Example 1
and the same measurement was conducted. As the result, in the black
image of the whole surface, a clear interference fringe was found
to be formed.
COMPARATIVE EXAMPLE 2
The same cylindrical aluminum as employed in Example 1 was
prepared, and the sand blast working was applied on the surface by
blasting spherical glass beads powder with an average diameter of
0.5 mm containing 18% by weight of spherical glass beads of 1 mm in
diameter under an air pressure of 9.5 kg/cm.sup.2. The sand blast
worked cylindrical aluminum surface was measured by a universal
surface shape measuring instrument "SE-3C" produced by Kosaka
Kenkyusho to find that the average surface roughness was 32
.mu.m.
On this substrate were formed successively the electroconductive
layer, the polyamide resin layer, the charge generation layer and
the charge transport layer to form an electrophotographic
photosensitive member for comparative purpose.
The electrophotographic photosensitive member for comparative
purpose was mounted on the laser beam printer as employed in
Example 1 and the same measurement was conducted. As the result,
although no interference fringe pattern appeared in the black image
of the whole surface, but black dots with diameters of 0.2 mm or
more were found to be formed at a rate of about 30/10 cm.sup.2 in
the 2000th sheet of the letter copy.
EXAMPLE 2
Ten grams of fine particulate zinc oxide (Sazex 2000, produced by
Sakai Kagaku K.K.), 4 g of an acrylic resin (Dianal LR 009,
produced by Mitsubishi Rayon K.K.), 10 g of toluene and 10 mg of an
azulenium compound represented by the following formula were mixed
thoroughly in a ball mill to prepare a coating solution for
photosensitive layer.
Azulenium compound: ##STR2##
The coating solution for photosensitive layer was provided to a
dried film thickness of 20 .mu.m in place of the photosensitive
layer of the layered structure comprising the charge generation
layer and the charge transport layer as employed in Example 1,
following otherwise the same procedure as in Example 1, to prepare
an electrophotographic photosensitive member.
The electrophotographic photosensitive member was mounted on the
laser beam printer employed in Example 1 (provided that the charger
and the developer were changed so that the charging may be of the
positive polarity and the toner of the positive polarity) and the
same measurement was conducted. As the result, no interference
fringe pattern was found in the black image of the whole surface,
with no black dot with diameter of 0.2 mm or more being found in
the copied letter of the 2000th sheet. Thus, very good images were
found to be obtained.
EXAMPLE 3
The surface of a cylindrical aluminum of 60 mm in diameter and 258
mm in length was subjected to sand blast working by blasting
spherical glass beads powder with an average diameter of 0.1 mm
containing 8% by weight of spherical beads of 0.2 mm in diameter
under an air pressure of 3 kg/cm.sup.2. The surface was measured in
the same manner as in Example 1 to find that its average surface
roughness was 3 .mu.m.
Next, 100 parts by weight of an electroconductive carbon paint
(Dotite, produced by Fujikura Kasei K.K.) and 70 parts by weight of
a melamine resin (Super-beckamine, produced by Dainippon Ink K.K.)
were dissolved in 100 parts by weight of toluene. The solution was
applied by dip coating on the aluminum cylinder subjected
previously to sand blast working, followed by heat curing at
150.degree. C. for 30 minutes, to provide an electroconductive
layer with a film thickness of 6 .mu.m thereon. The average surface
roughness of this electroconductive layer was measured similarly as
in Example 1 to be 2 .mu.m.
Subsequently, on the electroconductive layer were provided
successively the polyamide resin layer (with a thickness of 4.5
.mu.m), the charge generation layer and the charge transport layer
as employed in Example 1 to prepare an electrophotographic
photosensitive member.
This was mounted on the laser beam printer as employed in Example 1
and images were formed similarly as in Example 1. As the result, no
interference fringe pattern appeared in the black image of the
whole surface at all, and no black dot was also found to appear at
all in the copied letter image of the 2000th sheet.
When an electrophotographic photosensitive member was prepared
according to the same procedure as described above except for
changing the film thickness of the polyamide resin layer to 1.5
.mu.m and the same test was conducted, the number of black dots was
found to be increased in the copied letter image of the 2000th
sheet.
COMPARATIVE EXAMPLE 3
On the cylindrical aluminum subjected to sand blast working
employed in Example 3 was applied mirror surface working. The
surface was measured according to the same method as in Example to
find that its average surface roughness was 0.2 .mu.m. Next, on the
cylindrical aluminum were provided successively the
electroconductive layer, the polyamide resin layer, the charge
generation layer and the charge transport layer to prepare an
electrophotographic photosensitive member for comparative
purpose.
The electrophotographic photosensitive member for comparative
purpose was mounted on the laser beam printer employed in Example 1
and images were formed similarly. As the result, interference
fringe pattern was found to appear in the black image of the whole
surface.
EXAMPLE 4
To 100 parts by weight of a methanolic solution of a phenol resin
(solid content 60%: Plyofen 5010, produced by Dainippon Ink K.K.)
were added 100 parts by weight of a methanolic solution of a
copolymerized polyamide resin (solid content 10%: Amilan CM-8000,
produced by Toray K.K.) and 12 parts by weight of a methanolic
solution of p-toluenesulfonic acid, followed by thorough mixing and
stirring. Then, the mixture was applied by the dipping method on an
aluminum cylinder of 60 .phi..times.258 mm and cured by drying at
100.degree. C. for 20 minutes to form a coating with a film
thickness of 5.mu.. When this cylinder was dipped in methanol
heated to 50.degree. C. for 5 minutes, the polyamide component in
the coating was dissolved away, thereby leaving only the phenol
resin coated surface having an unevenness with an average surface
roughness of about 1.mu.to remain on the cylinder. The reflection
characteristic of the cylinder was measured to find that the total
light-diffusion reflectance was 66%. The average surface roughness
was measured by means of a universal surface shape measuring
instrument "SE-3C" produced by Kosaka Kenkyusho, and the ratio of
the intensity of total diffusing reflected light relative to the
incident light (total light-diffusing reflectance) was measured by
means of "Uvidec-505" produced by Nippon Bunko K.K.
Next, an aqueous low fat casein (produced in New Zealand) was
applied similarly by dipping to provide a casein resin layer on the
above coating.
As the next step, 100 parts by weight of .epsilon.-type copper
phthalocyanine (produced by Toyo Ink K.K.), 50 parts by weight of a
butyral resin (Eslec BM-2, produced by Sekisui Kagaku K.K.) and
1350 parts by weight of cyclohexanone were dispersed in a sand mill
dispersing machine containing 1 mm .phi. glass beads for 20 hours.
The dispersion was diluted with 2700 parts by weight of methyl
ethyl ketone and applied by dip coating on the above polyamide
resin, followed by drying by heating at 50.degree. C. for 10
minutes to form a charge generation layer with a coated amount of
0.15 g/m.sup.2.
Then, 10 parts by weight of a hydrazone compound having the
following formula: ##STR3## and 15 parts of a styrene-methyl
methacrylate copolymer resin (trade name: MS 200, produced by
Seitetsu Kagaku K.K.) were dissolved in 80 parts by weight of
toluene. The solution was applied on the above charge generation
layer and dried by hot air at 100.degree. C. for one hour to form a
charge transport layer with a thickness of 16.mu..
The thus prepared electrophotographic photosensitive member was
mounted on Canon laser beam printer (LBP-CX, produced by Canon
K.K.) which is a reversal developing system electrophotographic
printer equipped with a semiconductor laser with an oscillated
wavelength of 778 nm, and then line scanning was conducted on the
whole surface to form an image of the whole surface with a black
toner image. As the result, no interference fringe pattern appeared
in the whole black image at all.
Next, the operation of forming letters as the image by line
scanning of laser beam following letter signals was repeated for
2000 times under the conditions of a temperature of 15.degree. C.
and a relative humidity of 10%, and the copied letter image of the
2000th sheet was taken out. When the number of the black dots with
diameters of 0.2 mm or more was measured in the copied letter
image, no black dot was found at all.
COMPARATIVE EXAMPLE 4
As the comparative test, Example 4 was repeated except that the use
of the phenol resin layer employed in preparation of the
electrophotographic photosensitive member of Example 4 was omitted,
to prepare an electrophotographic photosensitive member.
When the electrophotographic photosensitive member for comparative
purpose was mounted on the laser beam printer employed in Example 1
and the same measurement was conducted, a clear interference fringe
was found to be formed in the black image of the whole surface.
COMPARATIVE EXAMPLE 5
The same aluminum cylinder as employed in Example 4 was roughened
on its surface according to the sand blast method. Next, on the
surface of the roughened aluminum cylinder, a casein layer of 1
.mu.m was provided directly with omission of the phenol resin layer
employed in Example 4. The surface was measured by a universal
surface measuring instrument "SE-3C" produced by Kosaka Kenkyusho
to find that its average surface roughness was about 2 .mu.m. The
total light-diffusing reflectance relative to the intensity of
incident light was then measured by "Uvidec-505" produced by Nippon
Bunko K.K. to be 46%.
The electrophotographic photosensitive member for comparative
purpose having the same photosensitive layer as in Example 4
provided on the casein layer was mounted on the laser beam printer
as employed in Example 4 and the same measurement was conducted,
whereby a clear interference fringe was found to be formed in the
black image of the whole surface.
COMPARATIVE EXAMPLE 6
The same cylindrical aluminum as employed in Example 4 was
prepared, and the sand blast working was applied on the surface to
an average surface roughness was 32 .mu.m, followed by provision of
a 1 .mu.m casein layer directly thereon with omission of the phenol
resin layer employed in Example 4. The total light-diffusing
reflectance relative to the incident light on this surface was
measured similarly as in Example 4 to be 68%.
When the electrophotographic photosensitive member for comparative
purpose having the same photosensitive layer as in Example 4
provided on the casein layer was mounted on the laser beam printer
as employed in Example 4 and the same measurement was conducted, no
interference fringe was found to be formed in the black image of
the whole surface, but 30 black dots with diameters of 0.2 mm or
more were found to be formed per 10 cm.sup.2 of the copied letter
image of the 2000th sheet, thus giving an image which can be viewed
with extreme difficulty.
EXAMPLE 5
Ten grams of fine particulate zinc oxide (Sazex 2000, produced by
Sakai Kagaku K.K.), 4 g of an acrylic resin (Dianal LR 009,
produced by Mitsubishi Rayon K.K.), 10 g of toluene and 10 mg of an
azulenium compound represented by the following formula were mixed
thoroughly in a ball mill to prepare a coating solution for
photosensitive layer.
Azulenium compound: ##STR4##
The coating solution for photosensitive layer was provided to a
dried film thickness of 21 .mu.m in place of the photosensitive
layer of the layered structure comprising the charge generation
layer and the charge transport layer as employed in Example 1,
following otherwise the same procedure as in Example 1, to prepare
an electrophotographic photosensitive member.
The electrophotographic photosensitive member was mounted on the
laser beam printer employed in Example 1 (provided that the charger
and the developer were changed so that the charging may be of the
positive polarity) and the same measurement was conducted. As the
result, no interference fringe pattern was found in the black image
of the whole surface, with no black dot with diameter of 0.2 mm or
more being found in the copied letter of the 2000th sheet. Thus,
very good images were found to be obtained.
EXAMPLE 6
A phenol resin layer was formed according to the same procedure as
in Example 4, except for changing the methanolic solution of the
phenol resin to 50 parts by weight and the methanolic solution of
the copolymerized polyamide resin to 150 parts by weight in the
mixture of the methanolic solution of the phenol resin and the
methanolic solution of the copolymerized polyamide resin.
The average surface roughness of this surface was measured
according to the same method as in Example 4 to be 8 .mu.m.
Further, the total light-diffusing reflectance relative to the
incident light was measured according to the same method as in
Example 4 to be 78%.
Further, an electrophotographic photosensitive member was prepared
by providing the same casein layer and the photosensitive layer as
in Example 4 on the phenol resin layer as described above, and the
same measurement as in Example 4 was conducted. As the result, no
interference fringe pattern appeared in the image at all when a
black image of the whole surface was formed. Also, when the 2000th
sheet of copied letter image was taken out for observation of
presence of black dot, no black dot was found to exist in the
letter image.
According to the electrophotographic photosensitive member of this
invention, no density irregularity in shape of an interference
fringe occurs after image exposure and developing, but a clear
electrophotograph can be obtained. Such an effect is marked,
particularly when employing a coherent light, above all laser, as
the light source for image exposure, and therefore it can be
utilized very advantageously as an electrophotographic
photosensitive member for laser printer.
* * * * *